'Ortho' is short for Orthochromatic - these films are desensitised to the red part of the visible spectrum which means (a) landscapes look wonderfully dramatic and (b) they can be handled under red safelight without fogging or over-exposure!
Ilford Ortho Plus 80 35mm Film
Rollei Ortho Film 120 B&W ISO 25
Silberra Orta 50 35mm Film B&W ISO 50
Rollei Ortho Film 35mm B&W ISO 25